Computerized tomography (CT), also known as computerized transaxial tomography, is recognized as a major breakthrough in x-ray technology. Sales of the equipment necessary to perform CT scans have risen sharply each year since their introduction in 1972. CT scans, by combining and integrating thousands of x-ray images simultaneously taken from a number of different angles around the body, produce cross-sectional images or "slices" of the body. The use of CT scans greatly improves density resolution of the resultant image over conventional x-rays, and, more importantly, it overcomes the problem of superimposition always inherent in a two-dimensional representation of a three-dimensional object.
One problem which has become apparent during the rapid development of CT scanning apparatus is that the contrast media preparations commercially available are not ideally suited for use therewith for several reasons. First, CT procedures utilize a high-energy x-ray source, i.e. peak energy levels in the 120-150 keV range and mean energy in the 50-80 keV range. Therefore, contrast preparations utilized in such procedures should ideally have a K-absorption edge in the 50-80 keV range. The preparations currently in use, which are principally insoluble salts of barium and iodinated lipids are not ideally suited for CT scans since they have K-absorption edges in the 30-40 keV range.
A second major disadvantage with most commercial preparations insofar as their use in CT procedures is concerned is their behavior in the intestinal tract. For example, the barium sulfate preparations present the pharmaceutical chemist a problem in obtaining uniform and stable suspensions of the highly insoluble barium salts which must be employed to avoid the toxicity of soluble barium preparations. Consequently the ability of radiographic preparations containing BaSO.sub.4 to achieve outlining of the bowel is dependent on the capability of suspending agents to cause the insoluble particulate material to adhere to the bowel wall. This problem is even more pronounced with certain barium sulfate preparations which have a tendency to agglomerate. This tendency materially detracts from their ability to uniformly coat the gastrointestinal tract.
The organic iodinated lipid preparations commercially utilized as contrast media are advantageous over the barium sulfate preparations in that they form homogeneous solutions. However, the iodine preparations have an even lower K-absorption edge than barium sulfate, a disadvantage in their use with the high-energy x-rays employed in CT studies. In addition, many iodine-containing preparations increase intestinal motility. This markedly detracts from the capability of such preparations to coat the intestinal mucosa and increases the rate at which they pass through the bowel. In addition, the increased intestinal motility caused by such preparations tends to form regional localized "puddling" in the intestinal tract lumen. Rapid passage of a contrast material through the bowel can be a distinct disadvantage for radiographic preparations since such preparations would only permit visualization of each segment of the bowel during only a short period of time.
In contrast to the aforementioned commercially available materials, preparations are realized in accordance with the present invention which, in addition to being stable and non-toxic, form aqueous solutions which are stable over the pH range encountered within the gastrointestinal tract and uniformly coat the intestinal mucosa, are uniformly distributed throughout the intestinal tract, do not increase intestinal motility and, most important, have a high K-absorption edge therefore being well suited for studies employing high-energy x-ray beams such as those used in CT studies.